External stop means for multi-turn potentiometer



Jan. 30, 1968 c. 1.. BUSH 3,366,910

EXTERNAL STOP MEANS FOR MULTI-'FURN IOTENTIOMETER Filed June 1, 1965 m w F13. 4!. f 29 378 H 38 37A A 3% INII'I'JN'I'UR. CECIL L. BusH P15- 2.

XAMM/MMMMJW United States Patent 3,366,910 EXTERNAL STOP MEANS FOR MULTI-TURN POTENTIOMETER Cecil L. Bush, Lebanon, Ind., assignor to Esterline-Angus Instrument Company, Inc., Indianapolis, Ind., a corporation of Delaware Filed June 1, 1965, Ser. No. 460,397 12 Claims. (Cl. 338149) ABSTRACT OF THE DISCLOSURE A multi-turn potentiometer with rugged external stop means to protect the internal stops. A stop pin fixed in a potentiometer mounting plate fixed to the potentiometer by jamb nuts. A second stop pin fixed in a retainer plate fixed to the potentiometer shaft and holding a stack of washers between the retainer plate and mounting plate. Circular grooves in opposite faces of the washers and extend-ing less than 360, the ends of the grooves serving as stops for stop slugs received in facing grooves of abutting washers and for the stop pins in the mounting and retainer plates, the slugs floating in the grooves between the stops, this arrangement facilitating rotation of the shaft in excess of 360 between limits imposed by the external stop means.

Background and description This invention relates generally to \multi-turn potentiometers having a rotatable input shaft, and more particularly to sturdy and reliable stop means which can be employed with many such potentiometers without modification thereof.

Potentiometers are frequently made in small sizes and of delicate construction. Many such potentiometers are of the multi-turn type, wherein more than one complete turn of the input shaft is required to obtain the complete range of resistance available with the potentiometer. This type of potentiometer typically has internal stop pins or other internal stop means to limit the rotation of the shaft after a certain number of turns in either direction. Frequently, however, the knob connected to or driving the potentiometer shaft is large, and it is easy for excessive turning force to be applied to the shaft through the knob. The result is that the internal stop means are damaged and the potentiometer is ruined.

It is therefore a general object of the present invention to provide improved stop means for potentiometers.

A further object is to provide external stop means adapted to employment with any of a variety of conventional potentiometer constructions.

A further object is to provide such stop means which are completely effective without in any way altering the construction of the potentiometer itself.

It is a further object to provide a stop construction which, although external to the potentiometer, requires very little space, and is relative immune to damage, and is easily incorporated.

Described briefly, a typical embodiment of the present invention, includes a potentiometer having a case mounted on one side of a mounting plate and a mounting stem extending through an opening in the cover plate and secured thereto in conventional manner by locknuts. A collar is received around the locknuts and serves as a piloting surface for a stack of identical stop washers.

Each of the stop washers has an arcuate groove in the front face thereof and an identical arcuate groove in the rear face thereof, these grooves being of a length less than 360 degrees. The stack of washers is axially retained in position against the front face of the mounting plate, by

means of an operating knob affixed to the potentiometer shaft.

Where two of the stop washers abut each other, at least portions of the arcuate grooves in the abutting surfaces are in registry. A solid cylindrical stop slug is provided in the registering portion and trapped therein. During relative rotation between one stop washer and the stop washer in abutment therewith, one end of one of the facing groove portions and one end of the other groove portion in registry therewith eventually come into abutting relationship with the stop slug, whereby relative rotation is thereupon terminated. Thereafter, rotational force is transmitted from the one stop washer through the slug to the other stop washer.

A stop pin is provided in the mounting plate and a stop pin is provided in the knob, these pins being received in the opposite end washers, whereby their rotations is limited. The lengths of the arcuate grooves are selected so as to limit the extent of rotational travel of the potentiometer shaft.

The functional portions of the stop pins and slugs are totally enclosed, and the stop washers have smooth outer cylindrical surfaces such that when stacked, an extended smooth cylinder is provided.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims:

FIG. 1 is an exploded side elevational view of components employed in a typical embodiment of the present invention, showing their relationship when disassembled in order.

FIG. 2 is a view of the assembly, with the principal portion of the combination being shown in a vertical section taken on a vertical plane through the axis, and only a part of the potentiometer itself being shown in section.

FIG. 3 is a front elevational view of one of the stop washers.

FIG. 4 is a section therethrough taken along the line 44 in FIG. 3 and viewed in the direction of the arrows.

Referring to the drawings in detail, the potentiometer 11 may be of well known construction such as that shown in US. Letters Patent No. 2,900,614 granted August 18, 1959, to Gach et al. The potentiometer includes a case 12 having an elongated resistance element 13 supported therein as a space wound helix. The potentiometer shaft is journaled in the case and has a portion 14 of rectangular cross section in the case, and a portion 16 of circular cross section projecting forwardly from the case. The shaft is rotatable on the axis 17.

An electrically nonconductive disc 18 is rotatable with the shaft and slidably keyed thereon for axial movement thereon. The periphery of the disc 18 is threaded as at 19 whereby, as the shaft 16 is rotated, the disc 18 is moved axially therealong, the threaded portion being received in the helix.

An internal stop arrangement for the potentiometer is provided by means of the pin 21 affixed to the disc and extending axially in the case, and an abutment 22 in the rear end wall of the case and an abutment 23 in the front end cover 24 of the case. Accordingly, as the shaft is rotated and the disc is moved axially along in the housing by the helical resistance winding, the travel of the disc, and thus rotation of the shaft, is limited by engagement of the front end of the pin with the front abutment 23 at one end of travel, and by the rear end of the pin with the rear abutment stop 22 at the other end of the travel. In one example, there may be five complete turns of the shaft between the starting point determined by the stop 23 and the stopping point determined by the stop 22.

Other details of this type of potentiometer may be found in the above mentioned patent, and they include electrical connecting means such as terminals 25, for example.

The front cover 24 of the potentiometer case has an externally threaded stem 26 received through an opening 27 in a mounting plate 28 such as a radio or instrument chassis, a shoulder 29 being provided on the cover 24 and fittingly received in the opening 27. The potentiometer is secured in place by the locknuts 31 and 32 .sandwiching the plate 23 between the potentiometer front cover 24 and the washer 33.

According to the present invention, a guide or piloting collar 34 is received around the washer 33 and locknuts 31 and 32, and has an outer cylindrical surface 36 coaxial with the shaft 16, for piloting purposes. Three identical .stop washers 37, 38, and 39 are provided in a stack, each of these stop washers having an aperture 41 therein received and piloting on the outer cylindrical surface 36 of the guide collar. These washers are rotatable on the collar and each of the washers has an arcuate groove in the front face thereof and an identical arcuate groove in the rear face thereof. For example, washer 39 (FIG. 4) has the arcuate groove 39A in the front face thereof and the arcuate groove 33B in the rear face thereof. Like grooves 38A and 38B are provided in stop washer 38, and grooves 37A and 37B are provided in stop washer 37. The arcuate extent of these grooves from end 42 to end 43 of groove 39A, for example, is approximately 350 degrees.

The stack of washers is retained in position so that the facing faces of adjacent washers are in abutting relationship, by means of the knob assembly 44 including the hand wheel 46, retainer plate 47 and hub 48, these three parts being atlixed together and secured to the shaft by a pin 49 or other suitable means.

A first stop pin 51 is affixed to the mounting plate 28 and projects forwardly therefrom. A second stop pin 52 is affixed to the retainer plate 47 and projects rearwardly therefrom. The stop pin 51 is received in the arcuate groove 37B of .stop washer 37, and pin 52 is received in the front groove 39A of stop washer 39. To limit the extent of relative rotation between adjacent stop washers, stop slugs 53 are provided. Each of these slugs is received partially in the rear groove of one stop washer, and partially in the front groove of the other stop washer next adjacent thereto. Each of the slugs is, therefore, trapped in registering portions of facing grooves and by abutting the end of the groove is able to transmit rotational motion between :stop washers.

In the operation of the device, beginning first with the knob hand wheel completely rotated counterclockwise so that front and rear stop pins 51 and 52 and the stop slug 53 engage the ends of the grooves in which they are disposed, the knob is rotated clockwise. This rotates the front stop pin 52 in its groove 39A until it reaches the opposite end of the groove. Then washer 39 is rotated by pin 52 until the first slug 53 encounters the ends of the rear groove 39B in stop washer 39 and the front groove 38A in stop washer 38, whereupon it begins to rotate the stop Washer 38. As stop washer 38 is moved in rotation, the slug between that and washer 37 will eventually engage the ends of the grooves 383 and 37A whereupon rotation of washer 37 will commence. Rotation of washer 37 will continue until it is stopped by the pin 51 abutting the end of the groove 37B. Thereupon rotation of the shaft clockwise will be stopped. The arrangement of the pins and lengths of the grooves is such that clockwise rotation will be stopped before the pin 21 of the internal stop in the potentiometer strikes either of the abutments. It is also constructed so that the external stop means of the present invention will stop counterclockwise rotation before the internal stop pin reaches the other stop. Therefore the external stop means of the present invention provides convenient means whereby action of the internal stops of the potenti- III ometer to stop shaft rotation is precluded, and there is no danger of the internal stop arrangement being damrnaged. Therefore the safe operation of the potentiometer itself without damage, is assured.

Because the stop washers are in abutting relationship with each other and the rear stop washer 37 is in abutting relationship with the front face of the plate, and the front stop washer front face is in abutting relationship with the rear face of the retainer plate, entrance of dust or dirt is prevented. The smooth external surfaces of the exposed parts of the external stop means assure that no interference with proper operation will occur, and a neat and compact, yet very rugged unit is obtained.

A variety of materials may be employed in the construction of the present invention. Delrin or nylon can be used, for example, for molding the stop washers. The slugs may be made of brass or stainless steel, for example.

While the invention has been disclosed and described in some detail in the drawings and foregoing description, they are to be considered as illustrative and not restrictive in character, as other modifications may readily suggest themselves to persons skilled in this art and within the broad scope of the invention, reference being had to the appended claims.

The invention claimed is:

1. The combination comprising:

a case;

a potentiometer shaft rotatable in said case and projecting outwardly therefrom;

electrical resistance changing means on said case and shaft and responsive to rotation of said shaft in said case to change resistance during rotation of said shaft through more than 360 degrees;

internal stop means inside said case to permit rotation of said shaft only between a starting point, and a stopping point a predetermined number of degrees, greater than 360 degrees, away from the starting point;

a mounting plate having an opening therethrough;

an externally threaded mounting stem affixed to said case and received through said opening;

a washer and lockouts received on said stem and affixing said case to one side of said plate, the portion of said plate bordering said opening being sandwiched between said case and said nuts, said shaft projecting through the center of said stem and coaxially therewith;

a piloting collar received on said washer around said nuts and having one end abutting said plate, said collar having an outer cylindrical surface coaxial with the shaft rotational axis;

a first stop pin afiixed to said plate and projecting forwardly therefrom parallel said axis;

a plurality of identical stop washers received on said collar and piloting on said cylindrical surface and rotatable thereon, each stop washer having an arcuate front groove in a front face thereof and an identical arcuate rear groove in the rear face thereof, the front groove being in alignment with the rear groove, and both grooves having end abutments approximately 350 degrees apart,

said stop washers being stacked so that facing faces thereof are in abutting relationship and portions of facing grooves are in registry,

the rear face of one of said stop washers abutting said mounting plate, said first stop pin being received and trapped in the rear groove of said one stop washer;

a stop slug received in the registering portions of each pair of facing grooves and trapped in the registering portions of both grooves of a pair to enable the slug to transmit rotational force from one stop washer to the abutting stop washer in one rotational direction when the slug reaches one end of each groove of the facing groove portions in which it is received, and to transmit rotational force in the opposite rotational direction from said one stop washer to said abutting stop washer when the slug reaches the opposite end of each groove of the said facing groove portions in which it is received;

a manual operating knob aflixed to said shaft and having means thereon axially retaining said stop washers in stacked relationship;

a second stop pin afiixed to said knob and received and trapped in the front groove of the stop washer nearest said knob;

the arcuate lengths of certain of said grooves being limited to permit rotation of said shaft within limits between said starting point and said stopping point, whereby limitation of shaft rotation by said internal stop means is precluded.

2. The combination comprising:

a case;

a shaft rotatable in said case on an axis and projecting outwardly therefrom;

internal stop means inside said case to permit rotation of said shaft only between a starting point and a stopping point a predetermined number of degrees away from the starting point;

a mounting plate having an opening therethrough;

a means afiixing said case to one side of said plate, said shaft projecting through said opening to a point beyond the other side of said plate;

a first stop member on said plate and projecting therefrom;

a plurality of stop wahsers coaxial with said shaft and rotatable on said axis, each stop washer having a front groove in a front face thereof and a rear groove in the rear face thereof,

said stop washers being stacked so that facing faces thereof are in abutting relationship and portions of facing grooves are in registry,

the rear face of one of said stop washers abutting said mounting plate, said first stop member being received and trapped in the rear groove of said one stop washer;

a stop slug received in the registering portions of each pair of facing grooves and trapped in the registering portions of both grooves of a pair to enable the slug to transmit rotational force from one stop washer to the abutting stop washer in one rotational direction when the slug reaches one end of each groove of the facing groove portions in which it is received, and to transmit rotational force in the opposite rotational direction from said one stop washer to said abutting stop washer when the slug reaches the opposite end of each groove of the said facing groove portions in which it is received;

means axially retaining said stop washers in stacked relationship;

a second stop member connected to said shaft and received and trapped in a groove of a stop washer other than said one stop washer;

the lengths of certain of said grooves being limited to permit rotation of said shaft within limits between said starting point and said stopping point, whereby limitation of shaft rotation by said internal stop means is precluded.

3. The combination comprising:

a multi-turn potentiometer including a case and a shaft rotatable about an axis in said case and projecting outwardly therefrom;

a first stop member external to said case and having a fixed position with respect thereto;

washer means coaxial with said shaft and having said shaft extending therethrough, said washer means being rotatable on said axis and having grooves therein;

said first stop member being received in one of said grooves;

a second stop member having a fixed position with respect to said shaft and received in another of said grooves;

the lengths of said grooves being limited to permit rotation of said shaft within limits whereby internal damage tot the potentiometer is avoided.

4. The combination comprising:

a case;

a shaft rotatable in said case on an axis and projecting outwardly therefrom;

an externally threaded mounting stem afiixed to said case;

a mounting member having a first stop member therea threaded fastener received on said stern and afiixing said mounting member to said case, to establish a fixed relationship between said first stop member and said case, said shaft projecting through said stem;

piloting means around said fastener and having an outer cylindrical sruface coaxial with the shaft rotational axis;

a plurality of stop washers piloting on said cylindrical surface and rotatable thereon, each stop washer having an arcuate front groove in a front face thereof and an arcuate rear groove in the rear face thereof, and both grooves having end abutments spaced apart,

said stop washers being stacked so that facing faces thereof are in abutting relationship and portions of facing grooves are in registry,

said first stop member being received in the rear groove of a first of said stop washers;

a stop slug received in the registering portions of each two facing grooves and trapped in the registering portions thereof to enable the slug to transmit rotational force from one stop washer to the abutting stop washer in one rotational direction when the slug reaches one end of each groove of the facing groove portions in which it is received, and to transmit rotational force in the opposite rotational direction from said the one stop washer to the abutting stop washer when the slug reaches the opposite end of each groove of the said facing groove portions in which it is received;

retainer means afiixed to said shaft and axially retaining said stop washers in stacked relationship;

a second stop member having a fixed relationship to said shaft and received in a front groove of a second of said stop washers;

the arcuate lengths of certain of said grooves being limited to permit rotation of said shaft through more than 360 degrees but within predetermined limits.

5. An external stop assembly, connectable to a device having a rotary adjustment shaft, and comprising:

a first mounting member mountable to a stationary portion of the device and having an aperture therethrough to accommodate the shaft of the device, said first mounting member having a first stop member thereon;

a second mounting member mountable to the shaft of said device, said second mounting member having a second stop member thereon projecting toward the first mounting member, the first stop member on said first mounting member projecting toward said second mounting member;

a stack of stop washer members disposed between said first and second mounting members, said washer members having grooves therein, the stop member of each of said mounting members being received in a groove of one of said washer members;

stop slug means disposed in facing grooves of washer members in said stack and freely movable between ends of the facing grooves, said mounting members and said washer members having smooth external 7 surfaces and fitting together to enclose said stop members and said slug means, whereby said stop members are completely enclosed. 6. An external stop assembly, connectable to a device having a rotary adjustment shaft, and comprising:

a first mounting member mountable to a stationary portion of the device and having an aperture therethrough to receive the shaft of the device, said first mounting member having first stop means thereon;

a second mounting member mountable to the shaft of said device, said second mounting means having a second stop member thereon;

washer means disposed between said first and second mounting members, said washer means having arcuate grooves in opposite faces thereof, said first stop means being received in one of said grooves and said second stop means being received in another of said grooves, said washer means being in abutting relationship with said first and second mounting members, enclosing said stop means, said washer means being rotatable with respect to said mounting members to an extent limited by said stop means, whereby upon securing said first mounting member to a stationary portion of said device and upon securing said second mounting member to the shaft of the device,

the extent of possible rotation of the shaft in the stationary portion, is limited. 7. An external stop assembly connectable to a device having a rotary adjustment shaft, and comprising:

a first mounting member mountable to a stationary portion of the device and having an aperture therethrough to receive the shaft of the device, said first mounting member receiving a portion of first stop means therein;

a second mounting member mountable to the shaft of said device, said second mounting member receiving a portion of second stop means therein;

a stack of washer members disposed between said first and second mounting members, end washer members of said stack receiving portions of said first and second stop means to limit relative rotation between said mounting members and end washer members, each washer member of said stack and the washer member next adjacent thereto both receiving portions of additional stop means to limit relative rotational movement therebetween, each washer member of said stack having a face abutting the face of the washer member next adjacent thereto around a circle of greater radius than the radial distance from the shaft to said additional stop means, and enclosing said additional stop means.

8. The stop assembly of claim 7 wherein:

said washer members have circular grooves in opposite faces thereof, said stop means portions being received in said grooves, and said grooves having stops therein engageable by the stop means portions received therein to limit relative rotation between each of said washer members and the washer member next adjacent thereto.

9. The combination comprising:

a multi-turn potentiometer including a case and a shaft rotatable about an axis in said case and projecting outwardly therefrom;

first stop means external to said case and mounted against movement relative to said case;

washer means coaxial with said shaft and having said shaft extending therethrough, said washer means being rotatable on said axis and having arcuate grooves in faces thereof, said grooves having stops therein and a first of said grooves receiving a portion of said first stop means, the said stop in said first groove being engageable with said first stop means portion to limit relative rotation of said washer means with respect to said case,

second stop means external to said case and mounted against movement relative to said shaft;

a second of said grooves receiving a portion of said second stop means, the said stop in said second groove being engageable with said second stop means portion to limit relative rotation of said washer means with respect to said shaft;

the stops in said grooves being located to permit rotation of said shaft in said potentiometer within limits whereby internal damage to the potentiometer is avoided.

10. The combination of claim 9 wherein:

said stops in said grooves are ends of said grooves.

11. The combination of claim 9 wherein:

said washer means are a plurality of washers placed together in abutting relationship in a stack, with additional stop means having portions received in facing ones of said grooves in abutting faces of each two of said washers, said additional stop means being engageable with said stops in said grooves to limit relative rotation of each washer of the two with respect to the other washer of the two.

12. The combination of claim 11 wherein:

said stop means are enclosed by said washer means.

References Cited UNITED STATES PATENTS 2/1959 Hatfield 74l0.2 X 12/1964 Hardison 338-149 X UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,366,910 January 30, 1968 Cecil L. Bush It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 58, "relative" should read relatively Column 3, line 52, "That" should read The Column 4, line 43, "lockouts should read locknuts Column 5, line 32, "wahsers" should read washers Column 6, line 8, "tot" should read to line 22,"sruface should read surface Column 7, line 11, "means" should read member line 12 "member should read means Signed and sealed this 24th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

